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The succulent, cylindrical leaves of the C4 dicot Portulaca grandflora possess three distinct green cell types: bundle sheath cells (BSC) Intracellular localization of enzymes was studied in organelles partitioned by differential centrifugation using mechanically ruptured mesophyll and bundle sheath protoplasts. Phosphoenolpyruvate carboxylase was a cytosolic enzyme in both cells; whereas, ribulose 1,5-bisphosphate carboxylase and NADP+-malic enzyme were exclusively compartmentalized in the bundle sheath chloroplasts. NADP+-malate dehydrogenase, pyruvate, Pi dikinase, aspartate aminotransferase, 3-phosphoglycerate kinase, and NADP+-triose-P dehydrogenase were predominantly localized in the chloroplasts while alanine aminotransferase and NAD'-malate dehydrogenase were mainly present in the cytosol of both cell types. Based on enzyme localization, a scheme of C4 photosynthesis in P. grandflora is proposed.Well confirm the suggestion made by Koch and Kennedy (Plant Physiol. 65: 193-197, 1980) that succulent C4 dicots can exhibit an acid metabolism similar to Crassulacean acid metabolism plants in certain environments.Plants possessing the C4-dicarboxylic acid metabolism of photosynthesis are characterized anatomically by having two photosynthetic cell types in the leaves, mesophyll cells and distinct bundle sheath cells (Kranz type leaf anatomy). The structure and biochemical function of these two types of leaf cells in C4 plants have been of much scientific interest over the past decade (3,17,20). Variations in leaf anatomy have been observed among C4 plants (17,19,21). The succulent dicot Portulaca grandiflora Hook has been reported as a C4 plant based on a measurement of 6 13C (24) and biochemical studies (7). Anatomically, the succulent cylindrical leaves of P. grandiflora, in addition to mesophyll and bundle sheath cells, have a third distinct type of green cell which is localized in the center of the leaves. These cells form the water tissue and contain scattered chloroplasts. There are many morphological and anatomical similarities between succulent C4 dicots and CAM plants. Recently, it has been reported that under certain environmental conditions, Portulaca oleracea, a succulent C4 dicot, is capable ofdeveloping an acid metabolism with many similarities to CAM (13,14). In this report, leaf anatomy and acid metabolism were studied in P. grandiflora. Protoplasts from the three cell types were isolated and key photosynthetic enzymes were located to determine their potential function in C4 photosynthesis. The results indicate that the succulent C4 dicot P. grandiflora has a slightly different Kranz leaf anatomy and enzyme compartmentation compared to other C4 plants and that it is also capable of an acid metabolism similar to that of CAM plants. MATERIALS AND METHODSPlant Materials. Plants of P. grandiflora Hook were grown from seeds in a greenhouse under a day/night temperature regime of 25 to 30/20 to 25 C and a light period of 15 h. Light was provided with Lucolux lamps (General Electric, Clevela...

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Abscisic acid inhibits shoot elongation of Scirpus mucronatus. -Physiol. Plant. 97: 1-4.The relationships between free ABA levels and shoot elongation were investigated in shoots of Scirpus mucronatus L. Under submergence, shoot elongation increased but free ABA levels decreased. The extent of the increase in length and the decrease in free ABA in submerged shoots increased with the increase of water depth. When the shoots were transferred to air after 12 days of submergence, they ceased to elongate and the free ABA levels recovered to the values of air-grown shoots. ABA, at concentrations from 1 ]iM to 1 mJW, inhibited the submergence-induced shoot elongation. In ambient air, fluridone, an inhibitor of ABA biosynthesis, at 7 ]iM decreased the free ABA levels in shoots but increased shoot elongation. The effects could be reversed by 10 ]iM ABA. These results indicate that ABA is an intemal inhibitor of shoot growth in Scirpus.